1) Field of the Invention
The present invention relates to a light source apparatus suitable for use in an optical communications system, as well as to a method for switching redundancy of the light source.
2) Description of the Related Art
In the field of optical communications systems, transmission capacity is increased through use of a Wavelength Division Multiplexing (WDM) technique. A semiconductor laser which emits a Continuous Wave (CW) of single wavelength has hitherto been widely employed as a signal source in a WDM system. With an increase in the number of channels, separate light sources must be provided in equal number to operational channels.
In order to implement a redundancy configuration for the case of occurrence of a failure in the light sources, a current light source and a backup light source must be provided for each working wavelength.
As mentioned above, constructing a WDM communications system through use of a light source which generates a single wavelength requires light sources which are equal in number to the operational channels. In order to fix the working wavelengths at channel intervals specified by the ITU-T (International Telecommunication Union-Telecommunication sector), temperature control and monitoring of a wavelength must be performed on a per-device basis.
In addition, in order to implement such a redundancy configuration through use of such a light source which generates a single wavelength, a redundancy configuration must be imparted to each of the light sources of respective wavelengths. Therefore, a footprint of the light sources and power consumed by the light sources become tremendous in association with an increase in the number of channels.
In a case where the redundancy configuration is implemented in the light source through use of the plurality of light sources provided in equal number to the operational channels, in the event that trouble has arisen in CW light (continuous light) generated from the respective light sources, a state in which no light is generated (a cutoff state) arises between a time when the trouble has been detected and a time when the switch is changed. Hence, a period of time during which the CW light is cut off is responsible for occurrence of a problem in communication, such as a transmission error.
Meanwhile, the super continuum light source, which is a technique for collectively generating an optical carrier ranging from hundreds of wavelengths to thousands of wavelengths, has recently been discussed. As compared with the light source, such as that described previously, which has a plurality of light sources in equal number to the operational channels, the SC light source involves simple temperature control. Further, with an increase in the number of channels, a footprint of the light sources and power consumed by the light sources do not become tremendous.
However, a redundancy configuration method for the case of occurrence of a trouble has not been put forward in relation to the SC light source. In a case where the WDM communications system is configured with the SC light sources, there is desired implementation of a redundancy configuration for making a switch to a backup light source system in the event that trouble has arisen in one light source system.
A technique described in Patent Document 1 provided below is available as a known technique relevant to the present invention. Patent Document 1 relates to an optical circuit which enables an improvement in product yield. Specifically, Patent Document 1 describes a multi-wavelength light source optical circuit into which are integrated a plurality of DFB lasers corresponding to optical elements.
[Patent Document 1]
Japanese Patent Laid-open2002-319731
However, the technique described in Patent Document 1 is intended for embodying a redundancy configuration for the case where the DFB lasers differ from each other in terms of an oscillation wavelength. Hence, the technique is not applicable to implementation of the redundancy configuration using the SC light sources, such as that mentioned previously.